Elastic fluid generator



Patented Nov. 13, 1934 ELASTIC FLUID GENERATOR Anthony J. Nerad, Schenectady, N. Y., assignor to g General Electric Company,` a corporation of New York Applicaties December 29, i992, serial No. 649,352 12 ciaims. (0,1.122-235) The present invention relates to elasticA fluid generators, that is, to apparatus comprising containers, drums or boilers, conduits and like elements for heating and evaporating a liquid.

More specifically, the invention relates to mercury vapor generators, for instance of the type described in the copending application of Emmet and Coulson, Serial No. 306,486, filed Sept. 17, 1928, although it is not necessarily limited thereto.

Apparatus of this kind comprise a furnace structure, a drum or drums, and heating units. The heating units are connected to the drum for receiving liquid therefrom and supplying vapor thereto. More specifically, these heating units '15 comprise a plurality of up-tubes located within the furnace and lining the wall thereof to form a wall screen. Liquid is circulated through these up-tubes by means of down-tubes which preferably are located external the furnace wall and are connected to the lower ends of the up-tubes. The upper ends of the latter are connected to the drum, preferably through the intermediary of a header.

The object of the present invention is to provide an improved elastic iluid generating arrangement in which certain difticulties met with in the use of a liquid like mercury,v owing to the high specic weights thereof, are overcome.

To clarify the problem on which this invention is based, attention is directed to the following physical facts The boiling point of any uid normally depends upon the pressure of the uid. The boiling point of water at a pressure of one atmosphere is 100o C. This statement, however, is true only with respect to water particles at the free surface of the water. A particle below this surface of the water being subjected to a co1- umn of water has a boiling'point above 100 C. because the fluid pressure is increasedA by the column of water. In other words, a liquid particle at a certain depth below the free liquid surface has a higher boiling point, because it is under higher total pressure. The rise in pressure of a particle at a certain depth below the free liquid surface does not only depend upon the length or depth from the free liquid'surface but also upon the speciiic weight of the liquid. The rise of the pressure with increasing depth from the liquid level is considerable in the case of mercury having a speciiic weight of about thirteen times that of water and we have therefore in mercury boilers a considerable rise in boiling temperature with increasing depth of the liquid. If we maintain, for example, a pressure of 140 lbs. gauge in a drum with a vapor temperature of 975 F., then the maximum temperature of 'the mercury rin vertically arranged boiler tubes of 5 ft. length will be approximately 1000o F. If we make the boiler tubes 10 ft. long instead of 5 ft. the boiling temperature would be 1025? F., 6,0 if 20 ft., 10'75 F., and for tubes of 40 ft.length the temperature will rise to 1150 F. The pressure at the bottom of the 5 ft. tube would be 165 lbs. per square inch gauge. The pressures in the longer tubes would be 190, 240, and 340 lbs. per square inch 'gauge respectively. With a definite temperature and pressure in a drum it is obvious that the stress in steel increases with the longer tubes owing to the higher Atemperatures and pressures under which a liquid evaporates in the lower portions of these tubes. It is well known that the resistance of steel to stresses de creases considerably with increasing temperature.

The capacity of an elasticfluid generating arrangement as heretofore -designed accordingly i5. can only be increased by spreading the heating surface in a horizontal plane, that is, by increasing the length and the width of the furnace. This, however, necessitates more floor space for the furnace which in many cases is not desirable or available. Thus the object of my invention is to provide an elastic iluid generating arrangement in which heating tubes, particularly wall screenheating arrangements of any desirable height or length, may be provided. This is accomplished in accordance with my invention by subdividing the wall screen tubes, that is, by the provision of a plurality of Wallscreen heating units at different heights. The units at a certain height or level are preferably provided with an independent header to, which liquid is supplied from vthe boiler drums through an overflow arrangement. In such an arrangement the static pressure of the liquid in each unit is determinedby the location of the header for the unit and is independent of the vertical distance between the header and the drum or a preceding header from which'the liquid is sup-l plied.

For a better understanding of what I believe t0 be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawing.

In the drawing, Fig. 1 illustrates an elastic fluid 105 generating arrangement embodying my invention; Fig. 2 illustrates a modification of such an arrangement; and Figs. 3 and 4 illustrate modifications of certain parts of the arrangements shown in Figs. 1 and 2. 110

In Fig. 1, where I have shown in section a front view of an elastic fluid generator such as may be used for producing mercury vapor, a drum 10 is provided with a plurality of liquid heating andv circulating tubes 11 connected to the bottom portion of the drum. Any suitable type of tubes may be provided, for instance, the kind described in my copending application, Serial No. 306,467, filed Sept. 17, 1928. Located within the drum is a block 12 for displacing a portion of the liquid to decrease the necessary amount of liquid for operating the boiler or generator. The parts so far described are located within a furnace structure comprising walls 13, 14. Heat is transmitted to the tubes and drum by radiation and conduction from any suitable source of heat, not shown. A conduit 15 serves for conducting vapor generated in the boiler to a consuming apparatus. Make-up liquid issupplied to the boiler by means of a conduit 16 connected to the drum 10. Y

In accordance with my invention I provide one or more heating units located at different levels below the level of the drum. In the present instance I have indicated three heating units'17, 18 and 19, each of which is provided with a header 20, 2l and 22 respectively. The headers are located at the upper end of the corresponding units. Liquid is supplied to the header 20 of heating unit 17 by means of a conduit 23, the conduit being arranged to stop or prevent the supply of liquid when the level in the drum 10 falls below a certain point, more specifically below the level existing under cold condition of the apparatus. With the arrangement embodied in Fig. 1 this is accomplished by connecting the upper end of conduit 23 to the drum at a point above thecold liquid level thereof. The upper end of conduit 23 projects into the drum and is connected to a baille-plate 24 located therein at apoint above the cold liquid level of the drum. The heating unit 17 also comprises a heating element 25 vertically arranged within the furnace wall and comprising a plurality of tubes, such asare shown for instance, in my Patent No. 1,866,367, filed Oct; 14, 1927, this element being termed hereafter up-tube. The upper end of the heating element or up-tube 25 is connected by means of a pipe or conduit 26 extending through the furnace wall 13 into the header 20 with its end located above the liquid level of the header. Thelower end of the up-tube is also connected to the header 20 by means of a down-tube 27 having a lower portion 28 kextending through the furnace wall. `The header 20 is partly iilled with liquid 29. During operation the liquid contained in the up-tubes is heated and partly evaporated. The differential pressure between the iiuid4 in the down-tubes and thek up-tubes thereby producedv causes the fluid in the up-tubes to flow into the header, whereas liquid flows from the header through the downtubes 27 into the up-tubes, to the effect that a circulation of liquid takes place. The liquid thus evaporated and conducted to the header 20 is conducted therefrom to the drum by means of conduits. 30 and 31 between the vapor space of the drum and the upper portion of the header. The liquid 29 in header 20 thus evaporates and is replaced by liquid supplied to the header from the drum through conduit 23. The supply through conduit 23 starts soon after the boiler is started, owingto the fact that a great amount of'liquid contained in the heating tubes 11 of the drum or drums is expelled therefrom and causesa rapid up-tube 33 connected to the header 21 in thev same manner as the down-tube27 and the uptube 25 are connected to the header 20. Liquid is supplied to the header 21 of heating unit 18 by a conduit 34 from the header 20 of the preceding heating unit 17. The conduit 34 is connected to the header 20 so that it permits the supply of liquid from header 20 to header 21 when the liquid level in header 20 rises above the cold liquid level and it prevents the supply of liquid when the liquid level in header 20 reaches the cold levelcondition. This is accomplished in the present instance by an overflow arrangement in `which the conduit 34 projects into the header 20 with its open end near the cold liquid level in header 20. Y

It must be realized that the functional relation between the heating unit 18 and the header 20 ofthe preceding heating unit is the same as the functional relation between the heating unit 17 and the drum `10. During operation, fluid is circulated through the tubes of the heating unit 18. The vapor thus vgenerated is conducted to the drum through a conduit 35 connected to an extension of conduit 30.

The heating element 19 comprises, besides header 22, a down-tube 36- and an up-tube 37 connected to the header. Liquid is supplied to the header through a conduit 38 forming an overflow arrangement with respect to the liquid contained in the header 21 of the preceding unit 18.

The vapor'produced in heating unit 19 is con-' ducted through an extension of conduit 30 to the drum. The operation of heating unit 19 is similar to that ofthe units described above and the functional relation between heating unit 19 and header 21 of the preceding unit is the same as that between heating unit 18 and theheader 20 or that between heating unit 17 and drum 10.

It will be readily seen that any number of heating units may be arranged at different levels without thereby causing an increase in pressure and temperature in the lower portions of these units, particularly the lower rends of the up-tubes 25, 33 and 37. This permits building elastic fluid generators of `any desirable height. Furthermore, the provision of independent headers for the mercury wall tubes permits the shortening of the tubes, resulting in a considerable saving in tubes and in liquid. With the lower pressure and temperature of the up-tubes, the stress in the steel from which these tubes are made is considerably reduced, resulting in prolonged life of these elements. n

In Fig. 2, where I have shown a modified embodiment of my invention, a drum 40, having a vapor discharge conduit 41, a liquid supply conduit 42, and a plurality of heating tubes 43, is provided in a furnace structure comprising walls 44. A heating unit 45 is arranged at a level below the level of the drum and comprises a header 46, a down-tube 47 and an up-tube 48 connected at their lower ends. The up-tube is vertically arranged within the furnace and has its upper end connected by a pipe 49 to the headerl 46.

Whereas in the arrangement of Fig. 1 the pipe 26 of heating element 17, corresponding to pipes 49 in this figure, extends into the vapor space of the header 20, I provide in the present instance the header with a baille plate 50 to prevent the lid@ up-stream of the fluid expelled from conduit 49 from interfering with the liquid flowing into the down-tubes 47. Liquid is supplied to the header 46 of the heating elementi45 by a conduit 51 between the header and the drum 40. 'I his conduit is provided with a liquid seal 52 for preventing vapor produced in heating unit 45 from flowing through this conduit into the drum. The vapor produced in heating unit 45 is conducted to the drum 40 by means of a conduit 53.

Whereas with the arrangement disclosed in Fig. 1 liquid flows from drum l0 to header 20 or from header 20 to the succeeding header 21, as soon as the liquid level of the drum 10 or the header 20 respectively rises above the cold liquid level, I provide in accordance with the embodiment of Fig. 2 means which permit a substantial rise of the liquid level in the drum beyond the cold liquid level. This has been done in the present instance by the provision of the conduit 53 of which the end connected to the header 46 comprises a plurality of branched portions 53% 53b and 53C extending into the header and ending at different heights above the cold liquid level in said header. During operation a rise of the liquid level in the header 46 causes a plurality of said branched portions to be cut 01T from the vapor space. In the drawing, for instance, I have indicated three branched portions of which two are immersed in the liquid space so that all the vapor generated by the heating unit 45 has to pass through the third branched portion. This necessarily causes a great drop in pressure or, from another viewpoint, a building up of pressure in the vapor space of the header 46, to the effect that liquid can only iiow from the drum 40 to the header 46 when the head above the connection of the drum with conduit 51 overcomes the differential pressure between the header 46 and the drum 40. From another angle, these branched portions of conduit 53 represent a means for increasing the resistance to flow of vapor in terms of rise of level in header 46, to the eiect that a level considerably higher than the cold liquid level may be maintained in the drum 40.

In Figs. 3 and 4 I have indicated two modications of certain parts shown in Figs. 1 and 2. In Fig. 3 a drum 54, corresponding to drums 10 and 46 in Figs. 1 and 2 respectively, is connected to a header 55, corresponding to headers 20 and 46 in Figs. 1 and 2 respectively, by means of a conduit 56. Whereas in th-e arrangements of Figs. l and 2 this conduit has its upper end connected to the corresponding drums above the cold liquid level therein, I have shown in Fig. 3 an arrangement in which the conduit 56 has its end connected to drum 54 below the cold liquid level therein. To prevent the conduit 56 from conducting liquid irom drum 54 to header 55 when the liquid reaches th-e cold liquid level, I provide conduit 56 with a portion 57 having its uppermost end above the cold liquid level.

In Fig. 4 I have shown another modiiication of this arrangement in which a conduit 58 connecting a drum or container 59 with another drum or header 60 includes l a check valve 6l. The check valve is forced towards closed position by a spring 62 which is adjusted so that the valve can only open with a static pressure on the valve obtained with a liquid level higher than the cold liquid level. In other words, liquid is only supplied from drum 59 to header 60 when the liquid level in drum 59 rises beyond the cold liquid level, the underlying feature of these different modiiications being the provision of conduit means for supplying liquid from a drum to a header or from one header to another and for preventing the supply of liquid when the levels in these elements reach a certain predetermined minimum height.

Having described the method of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In an elastic fluid generating arrangement of the type in which a iixed quantity of fluid is sealed in the system and stands at a predetermined level when cold, a container for liquid to be evaporated, a heating unit located below the level of the container, and' conduit means connecting the unit to the container at a point above the cold liquid level of the container for conducting liquid from the container to the unit in response to level changes in the container, the heating unit comprising a header inl which the cold liquid stands at an intermediate point so 1 as to provide a liquid space and a vapor space, down-tubes connected to the bottom of the header and up-tubes connected to the lower ends of the down-tubes and communicating with the vapor space in the header whereby the static liquid pressure in the up-tubes is independent from the static liquid pressure in the container and said conduit means.

2. In an elastic fluid generating arrangement of the type in which a fixed quantity of fluid is sealed in the system and stands at a predetermined level when cold, a container for liquid to be evaporated, a heating unit located below the level of the container and including a header its iii-ii in which the cold liquid stands at an intermef diate point so as to provide a liquid space and a vapor space therein, conduit means for connecting the unit to a point of the container above the cold liquid level of the container, and a furnace casing, the unit comprising a down-tube -;I`.'.

located outside the casing and up-tubes located within the casing, the up-tubes projecting into the vapor space in the header, the down-tubes being connected between the bottom of the header and the lower ends of the up-tubes 3. In an elastic fluid heating arrangement of the type in which a iixed quantity of fluid is sealed in the system and stands at a predetermined level when cold, a drum for containing liquid to be evaporated, a heating unit located A1,

below the level of the drum, a conduit for conducting vapor generatedin theunit to the vapor space in the drum, and a conduit connected to the drum above the cold liquid level thereof for conducting liquid from the drum to the unit, the unit including a header in which the cold liquid stands at an intermediate point so as to provide a liquid space and a vapor space in the header and heating elements with vertically arranged up-tubes having upper ends communicating with the vapor space in the header and downtubes connected to the bottom of the header and thelower ends of the up-tubes.

4. In an elastic fluid generating arrangement of the type in which a fixed quantity of fluid is sealed in the system and stands at a predetermined level when cold, a container for liquidto be evaporated, a heating unit located below the level of the container and including a header in which the cold fluid stands at an intermediate 'tainer at a point above the cold liquid level of point so as to provide a liquid space and a vapor space, conduit means for conducting liquid from the container to the header in response to the riseuof the liquid'level in the container vabove the cold level therein, the unit comprisingvertically arranged down-tube and up-tubes connected to the header with the up-tubesV communicating with the vapor space in the header and the down-l tubes connected between the bottom of the header and the lower ends of the up-tubes.

5. .In an elastic fluid generating.; arrangement of the type in which a fixed quantity of iiuid is sealed in the system and stands at aA predetermined level when cold,` a drum for containing liquid to be evaporated, a plurality of heating units located at different heights, each unit including a headerin which the cold liquid stands at an intermediate point so as to provide a liquid space and a vapor space, and generating tubes connected to the header, the upper heating yunit being located below the level ci the drum, a conduit connected to the drum at a point above the cold liquid level in the drum for `conducting liquid from the drum to the upper header, each of the succeeding headers ci the different units being connected to the headers of the preceding units at points above the cold liquid levelsv in the corresponding headers for conducting liquid from the upper header to the succeeding headers,

6. In an elastic fluid generating arrangement of the type in which a fixed quantity of iiuidis sealed in the system and stands at a predetermined level when cold, a plurality of containers for liquid located at different levels and having fixed cold liquid levels, a heating unit foreach container, means for supplying make-up liquid to the uppermost container, means for. supplying make-up lliquid to the succeeding containers comprising conduit means connecting each of the succeeding containers to the preceding container at a point above the cold liquid level of the preceding container.

' 7. In an elastic uid generating arrangement of the type in which a fixed quantity of fluid is sealed in the system and stands ata predetermined level when cold, a container for liquid to be evaporated and having a fixed cold liquid level, a heating unit located below the level of the container, and conduit means comprising a liquid seal for connecting theunit to the conthe container, said heating unit comprising a header, substantially vertically arranged do-wntubes receiving liquid from the header and vertically arranged up-tubes receiving liquid from the down-tubes and having their upper ends communicating with the vapor space in the header. v

l8. In an elastic fluid generating arrangement of the type in which a fixed quantityof fluid is sealed in the system and stands at a predetermined level when cold, a container .for liquid to be evaporated, a heating unit having a header and heating elements connected to the header and being located below the level of the container, the header having a liquid space and a vapor space, a conduit for conducting liquid from the container to the'header, and a conduit having one end connected to' an upper portion of the container and another end having a plurality of portions communicating with vthe header'r at different heights above the cold liquid level in the header.v

9. In an elastic' fluid generating arrangement of the type in which a fixedfquantity of fluid is sealed in the systemandstands at a predetermined level when cold, a container for liquid to be evaporated, a heating unit having a header and heating elements connected to the header and being located below 'the level of the container, the header having a liquid space and a vapor space, a conduit for connecting the headerl to the container at a point above the cold liquid levelof the container, and a conduit having one end connected tothe container and another end comprising a plurality of branched pipes projectng into the header and ending at different heights above the cold liquid level in the header for increasing the resistance to flow of vapor from the .header to the container with rising liquid level in the header whereby the liquid level in the container may be maintained above the connection of the first-named conduit with the container. Y 'i 10'. In an elastic fluid generating arrangement of the typein which a fixed quantity of fluid is sealed inthe system and stands at a predeterminedlevel when cold, a plurality of containers fornliquidto be evaporated being located at different' levels, means for conducting make-up liquid from the irst container to the second container'located at a lower level in response to the rise of the level in the iirst container, heating elements comprising vertically arranged down-tubes andup-tubes connected to the secondcontainer, the up-tubesbeing vertically ar-` ranged and having their upper ends communieating with the second container at a point above the liquidlevel in the second container and the down-tubes being connected between theV bottom of the second container and the lower ends of the up-tubes. i

v 11. In lan elastic fluid generating arrangement of the type in which a fixed quantity of fluid is sealed in the system and stands at a predetermined level when cold, a plurality of containers for liquid to be evaporated being located at `different levels, heating elements for each ci the containers, means for conductingk make-up liquid Yfrom the first container to the second container in response to the rise of the level in the first container, and means causing the level in the rst container to rise in response to increasing vapor pressure in the second container.

12. In an elastic uid generating arrangement of the type in which a fixed quantity of iiuid is sealed in the system and stands at a predetermined level when cold, a plurality oi containers for liquid to be evaporated being located at different levels, heating elements foreach of thev containers, means for conducting make-up-liquid from the first container to the second container located at a level lower than said iirst container in response to the rise of the level inv said first container, the means for conducting liquid having a seal for preventing the flow of vapor therethrough, and vapor discharge conduits connected ANTHONY J. NERAD. 

